myExistingArray (size=99999 VERY BIG)
      public 0 => 
        array (size=3)
          'key1' => string '15504' 
          'key2' => string '20'
          'count' => string '1'
      public 1 => 
        array (size=3)
          'key1' => string '15508' (length=5)
          'key2' => string '20' (length=2)
          'count' => string '2' (length=1)
      public 2 => 
        array (size=3)
          'key1' => string '15510' (length=5)
          'key2' => string '20' (length=2)
          'count' => string '5' (length=1)
....many more similar items

我想将它转换为一个非常简单的数组,其中来自“key1”和“key”的前值被连接成一个新的键,指向相应的“count”值,如下所示：

myNewArray (size=99999 VERY BIG)
      <key1>_<key2> => <count>
      15504_20 => string '1' (length=1)
      15508_20 => string '2' (length=1)
      15510_20 => string '5' (length=1)

性能对我来说非常重要,因为外部阵列有几千个项目. PHP中有快速方法吗？我得到的唯一的东西是一个简单的迭代,但这对我来说似乎很慢：

// works but I am looking for a faster version
$myNewArray = array();
foreach ($myExistingArray as $item) {
  $myNewArray [$item["key1"]."_".$item["key1"]]=$item["count"];
}

编辑/基础问题

有些人正确地补充说我当前的解决方案已经在O(n)中并且提到PHP中没有内置函数来加速这个.

我从MysqL数据库查询中获取“myExistingArray”.我基本上有工作对象,并希望按状态和event_id对它们进行分组.查询与此类似：

select count(job.id) as count,job.status as key1,job.event_id as key2
from job
group by job.status,job.event_id

我想重新排列密钥,以便稍后我可以轻松访问具有特定状态的特定事件的作业计数.